Answer:
The domain is 
Step-by-step explanation:
Given functions
and 
Subtract these two functions:

Plot these difference on the coordinate plane (see attached diagram). This function is defined for all vlues of x, so the domain is 
Combine like terms-- you can combine the k's:

Now you have:

Simply divide both sides by 2.5 to find the value of k:
The amount of percentaile of 600 to 6 is 1%
Answer: 2x-3=15
2(9)-3=15
18-3=15